I grin like an idiot when I'm dancing (and did when I competed in dance) because I love dancing and I love performing. But I hear you, ee. I think there are expression-related behaviours that can be learned. They can also become reflexive, IME.

The conclusion that I am coming to, albeit slowly, is that the word expression is being used in multiple ways,even in this one thread. Facial expression. Emotive-ness. Behaviours during performance. Characterisation of a dance.

Mostly because you can talk about it from two perspectives: the one expressing it and the one observing it. A brilliant actor can express emotion so effectively that you have no idea whether they are feeling it or not - and, likewise, they do the same thing to themselves! Small wonder actors often have tortuous love lives